1. Field of the Invention
The present invention relates to identifying secured containers for inventory and integrity monitoring purposes.
2. Introduction
To address heightened security concerns, governmental agencies require means to seal intermodal cargo containers and determine whether the seal has been compromised during transport. One conventional container-sealing solution is a bolt lock. Once locked, the bolt must be cut to break the seal. The bolt can be stamped with an identification number. This simple solution is inadequate because a cut seal can be replaced with one that is easily forged with the same identification number. Also, this solution is not compatible with automation.
Another conventional solution involves using a modified bolt lock in conjunction with an active radio frequency identification (RFID) tag. The bolt slides through the door lock and into a housing containing the tag electronics and bolt-sensing circuitry. The bolt has an insulating layer with an outer conductive layer that electrically connects to the bolt steel at the exposed end only. This design presents a short circuit to the sensing circuitry when the bolt is intact and an open circuit when it is cut at the exposed end. When the open-circuit condition is detected, the electronics records the event and an alert is transmitted the next time the seal is interrogated by an RFID reader. A second RFID tag is used to identify the container. Association between the container and the seal is made at the system level.
Although this solution accommodates automation, it requires two active tags per container, which presents an undesirable cost issue. In addition, the seal mechanism can be overridden by artificially creating a short across the contacts to the bolt-sensing circuitry prior to cutting the bolt.